MI5 is devoting more resource to countering state threats than during the Cold War, the head of the intelligence service has said, as he labelled Russia "aggressor number one".
He said MI5's successes in identifying and expelling Russian spies from the UK had left the Kremlin dependent on paying proxies for attempted attacks.
Sir Ken did not mention arrests at RAF Fairford directly, where Prime Minister Andy Burnham has said an alleged plot was "almost certainly directed by Iran's Islamic Revolutionary Guard".
Sir Ken continued: "These risks are real.
" Sir Ken said extreme right-wing terrorism tended to "skew young", driven by the internet - adding that MI5 had in recent months investigated a "radicalised extreme right-wing 13-year-old here in the UK".